I have a field grade (regular) 12 gauge. I replaced left and right hammer springs that were broken (long end up).The locking rod cam turns to move hammer back but the sears will not move up to lock into the hammer. The hammers move far enough but the sears wont move . You can manually move them to lock the hammer but they will not move mechanically. This is a pawn shop gun and well used.Both lock plates are free of grease and dirt and parts move freely. Any ideas??